Halftone prints are produced from bi-level images that indicate the presence or absence of ink at a particular location within the image. Variation of halftone dot sizes controls tonal values within a clustered-dot halftone print. For example, smaller dots produce lighter shades and larger dots produce darker shades.
A halftone image file can be viewed as a bitmap. Each bit is used to indicate whether a pixel is on or off. Color halftone printing devices make use of different channels, e.g., Cyan (C), Magenta (M), Yellow (Y), and Black (K), to define colors. Thus, color halftone prints may include a plurality of monochromatic bitmaps. Each monochromatic bitmap defines the presence or absence of dots for a particular channel.
Thermal halftone proofing systems, such as the Kodak Polychrome Graphics (KPG) Matchprint Digital Halftone proofing system and Kodak Approval proofing system, provide the ability to check geometric and colorimetric accuracy of halftone bitmaps prior to the creation of printing plates. The cost of consumables for such systems, however, can be high relative to that of inkjet printers. There are a number of commercially-available software packages that attempt to produce clustered-dot halftone prints on inkjet printers. However, the printed output from such packages can suffer from artifacts such as false moiré, graininess, or failure to reproduce the halftone screen ruling of the original image.